1. Field of the Invention
The present invention relates to a phase adjustment device for adjusting a phase (timing) of a pulse used for obtaining an image in a digital camera and a digital camera provided with the phase adjustment device.
2. Description of the Related Art
A digital camera (digital still camera, digital video camera, mobile telephone provided with a camera and the like) is configured such that an analog imaging signal obtained by an imaging element such as CCD or an MOS sensor is converted into a digital imaging signal, and the converted digital imaging signal is subjected to predetermined processing and then recorded. In order to obtain an image of a photographic subject using the imaging element, a pulse for driving the imaging element and a pulse for detecting a signal level are necessary. The phases (timings) of these pulses cannot be easily adjusted in a hardware designing process due to some variability generated in a manufacturing process. Therefore, the phase adjustment is performed by an engineer after the manufacturing process, and information relating to the adjusted phases (phase information) is stored in a memory region. At the time of actual use, the phase information is read from the memory region, and the phases are optimally set based on the read phase information.
In the field of a hospital-use camera, it may be necessary to exchange an imaging element. When an imaging element is replaced with another, the phase of the driving pulse is inevitably changed. Therefore, the phase adjustment is performed again. However, the imaging element cannot be easily exchanged in the case where an engineer has to readjust the phases.
FIG. 11 shows an example of a conventional phase adjustment device which successfully solved the foregoing problem. Referring to reference symbols shown in FIG. 11, 1 denotes an optical lens, 2 denotes an imaging element such as CCD (Charged Coupled Device), 3 denote a correlated double sampling unit, 4 denotes an automatic gain controller, 5 denotes an AD converter, 6 denotes a timing generator, 7 denotes a vertical driver, 10 denotes an analog front end, 20 denotes a DSP (Digital Signal Processor), 31 denotes a memory (SDRAM), 32 denotes a luminance level detector, 33 denotes a dispersion calculator, 34 denotes a timing adjuster, Sa denotes an analog imaging signal, and Sd denotes a digital imaging signal.
Whenever a phase optimal for conditions is changed due to environmental changes such as temperature change at the time of actual use, it is necessary to performance phase adjustment. The phase adjustment is performed mainly by the luminance level detector 32, dispersion calculator 33 and timing adjuster 34.
The luminance level detector 32 detects a luminance level in the digital imaging signal Sd of a plurality of pixels in a first pixel region for which the luminance level is to be detected, and supplies the detected luminance level to the timing adjuster 34. The timing adjuster 34 performs the phase adjustment of a pulse based on the received luminance level. More specifically, the timing adjuster 34 performs the phase adjustment for a peak sample pulse DS2 for sampling a signal component which peaks in a signal period and a reference sample pulse DS1 for sampling a signal component which is used as a reference in the correlated double sampling.
The dispersion calculator 33 calculates dispersion showing signal variability among a plurality of pixels in a second pixel region. The dispersion calculator 33 supplies the calculated dispersion to the timing adjuster 34. The timing adjuster 34 further performs the phase adjustment of a pulse based on the received dispersion. More specifically, the timing adjuster 34 performs the phase adjustment for an AD clock signal ACK which is an operation clock when the analog imaging signal Sa is AD-converted into the digital imaging signal Sd.
In recent years, however, the pulse which drives the imaging element increases its speed as the number of the pixels in the imaging element is increased, which makes it difficult to optimally adjust the driving and detection pulses. This recent trend created a new problem that a moving image cannot be obtained within a time range allowed for to perform the phase adjustment in a signal processing. Without the conventional technology quoted earlier or the conventional technology recited in the disclosed Japanese Patent Document (No. 2005-151081 of the Japanese Patent Applications Laid-Open), it is difficult to perform the phase adjustment in real time while obtaining images.